1. Field of the Invention
The present invention generally relates to Ethernet physical layer device (PHY) communications systems, and more specifically to channel designation within such a system.
2. Related Art
A conventional Ethernet communications system includes an Ethernet PHY device having a transceiver that can transmit signals or data over a wire or cable to another Ethernet PHY device that receives the transmitted signals or data. The transmitting PHY typically converts a digital signal to an analog signal (e.g., using a digital-to-analog converter (DAC)) prior to providing the signal to the cable. The receiving PHY typically converts the received analog signal back to a digital signal (e.g., using an analog-to-digital converter). The cable is typically an unshielded twisted-pair cable (usually copper) that typically contains four twisted pairs within its sheath. The PHYs and cable are capable of transmitting and receiving the signals or data at a wide range of different speeds, including the typical 10BaseT, 100BaseT, and 1000BaseT (Gigabit) speeds.
The twisted pairs of a cable correspond to channels. Therefore, in a cable with four twisted pairs, there are four channels. In both 10BaseT and 100BaseT communications, transmission is done on one twisted pair (i.e., a first channel), and reception is done on another twisted pair (i.e., a second channel), leaving two channels unused. With Gigabit communications, however, there is simultaneous bidirectional transmission over all four channels. Therefore, with Gigabit communications, channel ordering is extremely important. Any misinterpretation of the channel order can cause a failure in link.
However, various problems can occur that will impede or prevent the proper functioning of a conventional Ethernet communications system as just described. These problems include a variety of cable impairments, board-level miswiring, or even intentional design practices. One example is that a wire inside the cable could be broken, leaving no connection on that twisted pair between a transmitting PHY and a receiving PHY on the other side. As a second example, the wiring inside of the cable could be incorrect. For instance, channel 1 of a transmitting PHY is expected to be connected to channel 1 of a receiving PHY, but is instead connected to channel 2. As a third example, a customer's or user's expectations with regard to chip pinout or connector placement for each channel could be erroneous, possibly making it necessary to rewire the user's board, which can be costly.
The consequences of miscoupling PHY interfaces in a communications system could result in an inoperable system, system failure, or malfunctioning or damaged equipment. In an effort to prevent or mitigate the effects of these occurrences, various solutions have been implemented. These solutions include automatic media dependent interface (MDI) crossover (auto-MDIX), Ethernet@wirespeed, and cable diagnostics.
Auto-MDIX can be used in a typical four-pair system to detect and reconfigure the order of either pairs 1 and 2 or pairs 3 and 4. Auto-MDIX can be useful in eliminating the need for crossover cables that may be utilized between two computers, for example. A drawback of auto-MDIX, however, is that since auto-MDIX is limited to reconfiguring only pairs 1 and 2 or pairs 3 and 4, it cannot handle other wiring configuration combinations. For example, auto-MDIX would not be able to correct coupling involving pairs 1 and 3, 1 and 4, 2 and 3, or 2 and 4. Auto-MDIX is also not useful when one of the two main cable pairs is physically impaired (e.g., by a short or open circuit). Auto-MDIX is used throughout the industry, but may have other various names.
Ethernet@wirespeed provides an algorithm that can detect conditions on a cable or at a PHY, and can alter a transmission that cannot be supported under the detected conditions. For example, Ethernet@wirespeed can automatically reduce a transmission speed (e.g., from 1000BaseT to 10/100BaseT) when optimal transmission cannot be maintained due to detected channel impairments. Ethernet@wirespeed is useful when channel characteristics have degraded but the channel is still required for providing communication. Drawbacks of Ethernet@wirespeed are that it cannot operate on a broken or damaged twisted pair, and it does not have the capability to reconfigure wire pairs in order to utilize other good pairs within the cable. For example, even though pair 3 or pair 4 may be unused, if pair 1 or pair 2 is damaged or broken, Ethernet@wirespeed does not have the capability to reconfigure pair 3 or pair 4 for communication.
Cable diagnostics can provide information pertaining to the characteristics and quality of a cable. For example, cable diagnostics can detect an open, short, or proper termination on the cable. In addition, cable diagnostics can determine the cable length and can provide information regarding the location of an impedance mismatch in the cable. However, cable diagnostics do not have the capability to determine whether the cable has been incorrectly installed. For example, cable diagnostics will not be able to detect or report that pair 1 has been swapped with pair 3. Thus, cable diagnostics may report that everything is satisfactory, even if pair 1 has been swapped with pair 3.
What is needed are Ethernet PHY communications system implementations that allow for correction of the miscoupling and/or misconfiguration of Ethernet PHY interfaces while overcoming the limitations of previous solutions.